Pot size to column diameter ratio

[johnb]

OK.........you're both pretty. But you both sound like a couple of politicians. The OP asked a "general" question. you've gone on and on about what you believe to be correct but not even given a hint of an actual answer. Yes some more info to give a precise answer was needed. Obviously neither I or the OP has the kind of knowledge that you both posses. your responses to us have been rather demeaning rather than offering any kind of help. I don't imagine he was asking for the all perfect answer. He just wanted something like: " This diameter / height column with this many plates or what ever you think would work (or so) to make this product and maybe even offer a recommendation for a product that requires something totally different".

So here is my layout at this time. Please don't spend a pile of time telling me how I was a fool to do what I have done, I am looking to improve. My operation works. I think it can be better. I have been open a little over a couple months now. I currently make Vodka like so many do and white whiskey that comes off at 175 to 180 proof. Now before anyone goes off about how that ain't Whiskey, the TTB says it's so, I report it as such. The Yankee pallet doesn't seem to be fond of 140 proof white dog so I make what people in my neck of the wood like and are willing to buy (more than once) so let's stay on task.

As I said before, I strip 300 gallons and get 50 ish gallons of low wines (30 to 35% ABV) I have two of those Groen pots I mentioned earlier. on one I have a 4" Hillbilly stills 4 plate column. It works well for the White Whiskey with the dephrag up and with it low I can get the proof down so that I can actually have a product to put in a barrel as well.

On the other I have the same thing but there are 8 plates / sight glasses and I can make 190. Both make a good product that I have had no problem selling and even in such a short time repeat customers. I'm kinda excited about that.

The challenge is that they are very slow. 24 to 28 hours to do a Vodka run and 16 to 18 for Whiskey. I have flooded each them once by over powering them. So that leads me to believe that I have adequate HP in heat to accommodate larger columns.

I would be delighted to have a dozen answers & the why's. That's the beauty of the forum. The exchange of ideas and then make up your own mind what is best for you.

So, now you know my present set up, I am actually looking at two columns to make two products, two stills. I like the sight windows, they look cool and impress customers when in action. If I can I would like to distill my low wines in something like 10 to 16 hours (or less). 28 hours of sleeping for 45 minutes at a time in order to check head temp taste etc just isn't going to be good long term for me.

Is that enough info to get a rough idea of what size hole I will be putting in my pots? I know there are probly a thousand answers to my question, I'm just looking for the first couple that come to mind. I realize there is no perfect solution.

[Silk City Distillers]

Geez, a politician? C'mon.

There isn't an easy answer to the question, and the minute somebody posts something that looks like one, two more people are going to jump in with why it's not the answer.

The speed of your still is governed by 3 things, column diameter, reflux ratio, and input power. Think of the column diameter are your speed governor. You can't push faster than the governor without causing all sorts of problems, entrainment flooding, or 'smearing' like Dehner mentions. Input power should be obvious, the more heat input to the boiler, the more vapor you can generate. Reflux ratio, however, is the speed bump. When you don't have enough column height to hit your target ABV, you need to increase the reflux ratio to compensate, and the penalty for this is lower takeoff speed. In your example, you are getting hit by 2 issues, not enough column diameter, and needing to push a higher reflux ratio to hit your vodka. 28 hours is off the charts though. What you don't have a problem with is power, you have more than enough.

On a packed column for a 60 gallon still, I'd go at least 4", for bubble cap trays I'd go either 6 or 8". 6" if I had 10+ trays for vodka/neutral, and 8" for a whiskey/rum column to be able to push for faster run times. That's just what I would do.

Theoretically, given identical design parameters, if you were able to scale your trays from 4" to 8", you would be able to run 4 times faster. 8 trays for a neutral is a bit on the low side, so if you are able to either add additional trays, or potentially a packed section, you should be able to hit your target ABV with less reflux, and potentially drive that time down further.

Adding a packed section to your vodka column will probably let you drive it a little faster, with a little less reflux, if adding additional trays isn't possible.

On the stripping still timing, I've never yet seen a setup that the product condenser wasn't the limiting factor on a strip run.

[stevea]

dwrich1020 and meerkat are on the mark, or close enough to not deserve any correction, tho' perhaps more detail.

Evaporation is a surface phenomena, related to area, when the vapor above the surface is below saturation; this is irrelevant in a still or an LP tank w/ 100% saturation level in the vapor.

In your still the issue become pressure of the vapor & relative vapor pressures. Despite comments to the contrary, all stills have a pressure gradient from top to bottom; otherwise the vapor would not flow out. Typically below 15kPa or ~2 PSI. It's low pressure, not ambient pressure. Even w/o plates there is gravity & mass acceleration, and any fluid flow (gasses are fluid - get a dictionary if you disagree) in a 'pipe' causes resistance (google "Reynolds number"). *IF* you poured a LOT++ of energy into your pot, then the restricted flow would increase pressure and decrease BP; but we are far far from that.

So the liquid sits just below the the vapor equilibrium temp (for the given pressure) and vapor evolves at a rate dependent on the amount or energy applied (the heat of enthalpy concept that dwrich1020 correctly introduced). The only 'alteration I'll suggest is that a ~9%ABV wash is around ~3% mole-fraction ethanol in the liquid phase and around ~25% mole-fraction in the vapor phase; so water isn't a perfect model for this enthalpy. That's why we have the vapor equilibrium charts. Still we can determine a vapor flow rate of vapor out to the condenser per unit power (watt) in.

Any basic ChemE text will explain that the problem with low vapor flow rate in a still is "weeping" The plates don't fill and so they don't create a new vapor/liquid equilibrium and you get poor separation. The problem w/ high vapor flow rates is that you get puking & flooding and these also cause poor separation. This problem doesn't magically disappear if you have packing instead of literal plates - the point is either you fail to create a new equilibrium by undeerflow or overflow.

I've done an analysis on some of the major-league pro columns and they seem to shoot for ~22-40 cm/sec vapor flow rate and that's a sort of upper bound - you can certainly go to lower rates if your plates are carrying adequate liquid. *MOST* columns operate in turbulent flow, and we small-timers have an advantage there.

===

No offense meant to anyone - sincerely - but I'm a bit tired of people hobby-experimenting trying to re-discover by experiment what has been know for 100 years.

[Skaalvenn]

I just have a question about the whole evaporation vs boiling in relation to surface area thing (because I'm curious and it's not an area of science that I fully understand).

Ok, so evaporation in itself is related to surface area? Cool, I get that. A drop of water evaporates a lot slower when it's in a drop than if it's smeared on a larger surface.

Boiling is related to the heat of the water temperature? Cool, I get that. Substances won't boil below their boiling temperature.

Evaporation doesn't occur when the surrounding "air" is saturated? Cool, I get that. Clotheslines don't work on humid days.

Now, here's where my question comes in.

Does evaporation in a fully heated and running still (assume any commercial sized--no theoretical sizes/shapes) have any sort of impact on it's output? We know a pot with water heated to 210 degrees is going to steam a lot more than one sitting at room temperature, especially if agitated. But, will it still steam to a large degree inside the running still?

Thanks

[johnb]

James:

chuckle........politicians......chuckle chuckle again...I'm not the only one.

Thank you for the input. I was not a chemistry major but I do have a grasp and understandings of the concepts. Thanks again for having the courage to actually have a few suggestions for me to investigate further and chew on. I understand the risk you just took trying to help and quite possibly taking pot shots for the effort. Bless you.

Steve:

Thank you for trying as well. I am afraid that much was above my head. Oh and btw, I have a DSP, I have a respectable operation and am doing my best to be better than I presently am. I am not a hobbyist. I really do respect your knowledge, I do desire to improve mine as well. That said, I am sorry that you are tired. Perhaps a nap is in order? (no offence intended)

[Mott Hill]

Dehner, What are your credentials for being an engineer? You understand that's a formal title earned with at least a bachelor's degree and then years of full time supervised employment, correct? It's an outlandish claim considering your attitude toward the information presented to you.

[Dehner Distillery]

Hello,

James is right on.

My option nothing against "hillbilly stills" but they are to short and to small diameter for what you are doing. A column that size are for starting out, but not full on production. You have to charge for your time when producing a product and it sounds like it takes you for ever.

1. as mentioned above because of your short column size you have to run a much higher reflux ratio

A= make the column taller, the farther the out put is from the boiler, the less reflux ratio

2. over taking the column, is because of high reflux, no drain on the duel flow trays, to small column because of vapor velocity.

We need to understand ways happening. "hillbilly still" uses a "duel flow tray", a duel flow tray is a sieve tray with no over flows. You can over take the column because the is a lot of liquid setting on the trays because of the high reflux, because of the liquid is wanting to go down and the vapor is going up at a high rate "vapor velocity" and the duel flow tray is flat, the pressure on the bottom on the equal not letting any liquid passed the vapor. The liquid starts to over take each tray.

A= Change tray design (install over flows, or interrupted duel flow design, or ect.) you could go with rings or saddles also, widen out column to lower pressure, widen out column to lower vapor velocity.

3. Long distilling times, a little of everything above.

A= taller column 6' min (5'column & 1' dephlegmator), wider column I'd say 8", interrupted duel flow tray ( or something with overflows) with a layer of 1/2" ceramic saddles and 1/2" copper pipe cut up.

Just trying to help.

take care.

[Roger]

Dehner, What are your credentials for being an engineer? You understand that's a formal title earned with at least a bachelor's degree and then years of full time supervised employment, correct? It's an outlandish claim considering your attitude toward the information presented to you.

I for one feel far more comfortable taking advise and direction from someone who is actually in the trade, producing both products and equipment, than someone who has a $80,000- piece of wallpaper.

[Mott Hill]

I for one feel far more comfortable taking advise and direction from someone who is actually in the trade, producing both products and equipment, than someone who has a $80,000- piece of wallpaper.

You've missed the point. The title of Engineer is worth something or else it wouldn't be written there. It lends weight to bad design advice.

I'd never suggest that a person can't take advice from whomever they like. If a guy wants to say he has X years of experience, or loads of common sense, that's honest and respectable. But falsely claiming credentials isn't acceptable behavior in professional circles. It's fraud. Standing on your own 2 feet is at least respectable.

Done here. I'm going to spend my time reading up on posts from the NASA qualified members.

[johnb]

Easy there boys. We all have our opinions. We are all big kids and can make our own decisions based on what we think will work best for ourselves. And mostly we all have different learning styles. Some, like myself learn by experimentation and doing. Others have a real gift imo to process the information in their head and are able to put it into practice without the time and cost of that experimentation. There are success stories & failures on both sides of that ledger.

Dehner: I too have nothing bad to say about the hillbilly still column (except I think the name could be improved) it is, what it is, and actually is making a very nice product that sells, and sells again. For me that's the point.

I started too small and now can not keep up with those sales (what a wonderful problem!) Your points are well taken, a bit of all of the above you wrote are in order for me. Take it to the next level as it were. I have a lot of homework ahead before a final decision is made. Thank you for your input. Good rubber meets the road stuff.

I didn't want to go too big, or not big enough (again) That's why I chimed in on this thread in the first place. All of you have helped me in your own way. I now have a pretty good idea to narrow down my scope of investigation and purchase. What ends up working for me certainly wont work for everyone. Then again it doesn't have to. In the end, you all have pointed me in the same direction.

Steve: I re-read what I wrote. I do get where you are coming from. Each of us are individuals with different learning styles. I wish I had your gift of understanding. My comments directed at you were a might snarky. Perhaps I am the one that needs a nap.

Merry Christmas everyone.

JB

[Max Action]

18 to 28 hours to distill 60 gallons of low wines isn't normal. With 13500 watts of heat, I know from personal experience you can distill that much low wines in less than 8 hours. I agree that increasing column diameter from 4" to 8" should help achieve that.

As for the controversy of pot diameter, I think the confusion lies with the fact that normal evaporation is dependent on surface area. It's certainly logical that a glass of water will take longer to evaporate than the same volume of water poured on the floor or other larger area. I'm sure that's true with propane tanks as well, but those are not boiling. Once you've reached the boiling point, the vapor pressure exceeds the atmospheric pressure, and surface area doesn't matter anymore. When it boils, all those internal bubbles are creating their own surface area, and it doesn't make a practical difference on how much area there is at the top of the liquid.

[stevea]

Why experiment when the result is well known ?

Evaporation occurs when molecules near the liquid surface of liquid have sufficient kinetic energy and correct trajectory to escape - to overcome weak binding energy (part of dwrich1020's enthaply) and become vapor. The rate of evaporation is related to the surface area, the amount of molecules with sufficient energy (think temperature) to escape at their particular trajectory.

Condensation occurs when vapor molecules strike a surface and condense rather than re-evaporate. This rate is primarily related to the concentration of these molecules in vapor phase (partial pressure) at a given temperature.

Evaporation and condensation rates are equal at the "vapor pressure" which is specific partial pressure (concentration of the specific vapor) and is temperature dependent. So the vapor pressure of water at 68F(20F) (called 100% humidity wrt weather) is 0.34psi(2.3kPa) of water vapor pressure at that temp (about 2% of atmospheric molecules as water). The vapor pressure of water at 212F(100C) is 14.7psi(101kPa) or one atmosphere (100% of molecules at standard pressure).

Boiling occurs when the vapor pressure is less than local pressure - even under the liquid surface, and 1 degree F will drive boiling down almost a yard deep into water (overcomes the water pressure at depth).

In a still pot at equilibrium near the boiling point, the evaporation and condensation are nearly equal - net zero or very close. That is the partial pressure of water in the headspace is essentially 1 atmosphere (all water vapor) which is the vapor pressure at 212F. So essentially all the vaporization of water is due to boiling in the still.

The amount of boil off is directly related to the energy applied as heat vs the enthapy (heat of vaporization) dwrich1020 mentioned. Unrelated to surface area.

[stevea]

Easy there boys. We all have our opinions. We are all big kids and can make our own decisions based on what we think will work best for ourselves. And mostly we all have different learning styles. Some, like myself learn by experimentation and doing. Others have a real gift imo to process the information in their head and are able to put it into practice without the time and cost of that experimentation. There are success stories & failures on both sides of that ledger.

Opinions are like a.... Facts are a different matter.

I agree wrt learning styles - but your still operates exactly the same regardless. There are some aspects of this biz that no textbook contains - certainty the realm of art and craft, but no one person has the ability to replicate the several centuries of experiments that lead to modern still design, and there is no need if you can crack a book open.

[meerkat]

stevea - a typo?

"Boiling occurs when the vapor pressure is less than local pressure"

should be

Boiling occurs when the vapor pressure is greater than local pressure